Xmodem protocol and the algorithmic realization in serial communication

摘要

Xmodem protocol of the error detection based on the Visual Basic 6.0 and its algorithmic realization in the serial communication is described in this paper. In the Automatic Meter Reading System of low voltage power carrier wave, the telecommunications of the data between upper computer and lower controller is transmitted over telephone network appended modem. Binary system data is disturbed easily by the line noise when it transmits over serial lines in the serial communications field. However, the disturbance can make one or more value of the character changed during the transmission. In order to assure that the long-distance transmission of the data is fast and reliable, Xmodem protocol of the error detection can assure that the data of receiving and sending is completely consistent. Xmodem protocol is a protocol of "receiving driven", Namely, the transmission of data block is started by receiver. The receiver judges when the improper data block is retransmitted and when too much errors are occurred so that the transmission of the file can't be continued, etc.. On the other hand, the sender prescribes the manner of packing and sending of the data. All data were divided into data block consisting of 128 bytes and were packed into data packet contained control information to transmit over serial links. The practice shows that Xmodem protocol is reliable, and can meet the requirement of data transmission in the Automatic Meter Reading System. So its application is quite widespread.